Methylation of aromatic hydrocarbons



Patented Aug. 24, 1948 "UNITED STATES PATENT OFFICE METHYLATION FAROMATIC KYDROCARBONS Louis Schmerling, Chicago, 111., assignor toUniversal Oil Products Company, Chicago, 111., a corporation of Delawarei No Drawing. Application March 31,1941.

Serial No. 386,110 1 24 Claims. (oi. 260-671) This invention relates tothe treatment of arcmatic hydrocarbons to produce methylated and 7chloride, produces sludge-like material, and prevents continuousoperation of the process.

Although it is known that composites of phosphoric acid and carrierscatalyze the alkylation of benzene by olefins or alcohols containing 2or more carbon atoms per molecule, it has hitherto been consideredimpossible to bring about the condensation of benzene and methanol inthe presence of such catalysts. The present invention is different fromthe prior art on this subject in that methylation of an aromatichydrocarbon as benzene by methanol or by another suitable methylatingagent is effected in the presence of a relatively stable granularcatalyst, namely a calcined composite of an acid of phosphorus and agenerally siliceous adsorbent such as diatomaceous earth.

In one specific embodiment the present invention comprises a process forproducing methylated aromatic hydrocarbons which comprises contacting anaromatic hydrocarbon with methanol under methylating conditions in thepresence of a calcined composite of an acid of phosphorus and agenerally siliceous adsorbent.

While the process of this invention is particularly applicable to theproduction of toluene from benzene, it may also be utilized forconverting other aromatic hydrocarbons into methylated andpoly-methylated aromatic hydrocarbons. Thus aromatic hydrocarbons whichmay be methylated under suitable operating conditions include benzene,toluene, other alkylated benzenes, naphthalene, alkylated naphthalenes,and other polynuclear aromatic hydrocarbons obtainable by thedistillation of coal, by the dehydrogenation of naphthenes, by thedehydrogenation and cyclization of aliphatic hydrocarbons as well as ofalkylated aromatic hydrocarbons, and by other I means.

Besides methanol, which may be formed by destructive distillation ofwood, by controlled oxidation of hydrocarbons, and by catalyticconversion of a mixture of carbon monoxide and hydrogen, other suitablmethylating agents include methylhalides, methyl ether, methyl esters,and other methoxy-containing organic compounds capable of reacting witharomatic hydrocarbons to yield a substantial proportion of methylatedaromatic hydrocarbons in the presence of a catalyst as hereinafter setforth.

When employing methyl compounds as methanol, dimethyl ether, and methylhalides as methylating agents, hypothetical methylene is probablyformed, which may be represented by the formula, =CH9, and possiblyserves as the active methylating agent. may herein be considered as thefirst member of the olefin series which undergoes reaction, for example,with benzene to produce toluene and poly-methyl benzenes while otheraromatic hydrocarbons may similarly yield other methylated aromatichydrocarbons. The different methylating agents, however, are notnecessarily equivalent in their action nor used under the sameconditions of operation to form desired products. 25

The essential ingredient of a granular catalyst which is employed tomethylate an aromatic hydrocarbon, according to the process of the p entinvention, is phosphoric acid which may constitute or more of thecatalyst mixture and in most cases is over 30% by weight thereof. 01?the various acids of phosphorus, orthoe or pyro-phos- 1 phoric acids aregenerally preferred on account of their methylating abilities, theircheapness, and the readiness with which they may be procured, althoughthe invention is not restricted to their use but may employ any of theother acids of phosphorus insofar as they are adaptable. It is notintended to infer, however, that the different acids of phosphorus whichmay be employed will produce identical eifects upon any givenmethylation reaction as each acid will exert its own characteristicaction. The methylating activity of a given catalyst is also dependentupon the ratio of acid to siliceous adsorbent contained therein.

Solid phosphoric acid catalysts, which are particularly utilizable inthe present methylation process, maybe made by mixing an acid ofphosphorus, such as orthoor pyro-phosphoric acid, with a finely divided,relatively inert and a generally siliceous carrier such as, for example,kieselguhr, to form a rather wet paste (the acid 500 6. to produce asolid cake; grinding and siz- For convenience methylene ing to produceparticles of usable mesh; and rehydrating the catalyst granules attemperatures of the order of 260 C. to produce an acid compositioncorresponding to the optimum methylating activity which usuallycorresponds approximately to the pyro-acid in composition.

This catalyst-preparation procedure may be varied by forming particlesfrom the original paste by extrusion or pelleting methods and followingwith the calcining and rehydrating steps. In the reactions taking placeduring calcination it is evident that some acid is fixed on the carrierand that some metaphosphoric acid, which is substantially withoutmethylating activity is formed. The rehydrating step evidentlyproducesan acid composition corresponding closely to the pyro-acid having aformula H4P2O1. Unless rehydration is practiced the temperature ofapproximately 300 C. should not be exceeded in the calcination step. Andif higher temperatures produce catalyst particles of greater structuralstrength, depending upon the character of the carrier :and thecomposition of acid fixed therewith, the composition of the acid may bebrought to the desired point by contact with superheatedsteam atapproximately 260 C. at atmospheric pressure. This brief description ofa solid phosphoric acid catalyst and of its preparation is notexhaustive, as both have been generally described already in U. S.Patents Nos. 1,993,512 and 1,993,513 and others. Solid phosphoric acidcatalysts are hygroscopic to a variable extent and are best ground,sized, and preserved for use out of contact with moist air.

Because of the possibility of varying both the active phosphoric acidingredients and its proportions with the relatively inert adsorbentmaterials which go to form the solid phosphoric acid catalyst masses, anumber of alternative catalysts exist each of which will have its ownparticular catalyzing character which will not be exactly equivalent tothat of the masses of diil'erent composition.

In the methylation of aromatic hydrocarbons by methanol or by anothermethylating agent. substantially any of the acids of phosphorus whichhave been found to promote polymerization of olefins or the alkylationof aromatic hydrocarbons with olefins may be employed as catalyst eitheralone or supported by a suitable carrier. Calcined composites of an acidof phosphorus and a'generally siliceous adsorbent which are usuallyreferred to by the term solid phosphoric acids are referable-in thatthey permit continuous methylation with a fixed bed catalyst. Othersuitable methylating catalysts include certain acid-acting salts ofphosphorus such as cadmium phosphate, copper pyrophosphate, calcium acidphosphate, and others.

In eflecting reaction between benzene or another aromatic hydrocarbonand a methylating agent as methanol according to the process of thepresent invention, the exact method of procedure varies with the natureof the reacting constituents as well as with the composition andactivity of the catalyst employed. A simple procedure which is used inmethylating benzene consists ,in contacting a mixture of benzene andmethanol with a solid phosphoric acid catalyst at a temperature of fromabout 350 to about 500 C. and preferably from about 350 to about 425 C.under a pressure of from substantially atmospheric to approximately 300atmospheres or more.

Intimate contact of the reacting components with the catalyst iseffected by passing the reaction mixture over a fixed bed of the solidphosphoric acid or the reactants may be mixed with finely divided orpowdered catalyst in a substantially fluid type of operation. Thereaction mixture undergoing treatment preferably contains between about1 and about 20 molecular proportions of benzene, or other aromatichydrocarbon per molecular proportion of methanol or other methylatingagent in order to diminish production of poly-methylated hydrocarbonsand to favor theproduction of toluene or of other monomethyl compoundswhen an aromatic hydrocarbon other than benzene is similarly treated.

Thus benzene and methanol are commingied and passed through a reactorcontaining the granular catalyst such as a calcined composite of an acidof phosphorus, or at least a portion of the benzene is charged to areactor while the methanol as such or preferably diluted by anotherportion of the benzene being treated, is introduced at various pointsbetween the inlet and the outlet of the reaction zone in such a way thatthe reaction mixture being subjected to contact with the granular solidphosphoric acid catalyst contains at all times a. relatively lowproportion of methanol and thus favors production of toluene rather thanthe formation of more-highly methylated aromatic compounds.

While the method of passing a methylating agent. as methanol, andbenzene or other aromatic hydrocarbon, either together or concurrently,through a suitable reactor containing a fixed bed of granular catalystis generally customary procedure, the interaction of methanol and anaromatic hydrocarbon may also be effected in batch type operationutilizing a closed vessel in which some of the reacting constituents arein liquid phase and in which the catalyst is present preferably infinely divided form and is maintained in dispersion or suspension bysome means of agitation. Reacting constituents may also be contactedwith the catalyst in mixed phase to effect a similar type of reaction.The choice of operating procedure is dependent upon such circumstancesas the temperature and pressure found to be most effective for producingthe desired reaction between a particular aromatic hydrocarbon and a.methylating agent as methanol.

In general the products formed by interaction of methanol with a molalexcess of an arcmatic hydrocarbon are separated from the unreactedaromatic hydrocarbon by suitable means as by distillation and theunreacted portion 01' the aromatic hydrocarbon originally charged andmethyl ether which may be formed from methanol are returned to theprocess and commingled with additional quantities of the mixture ofmethanol and aromatic-hydrocarbon being charged to contact with thecatalyst. Thus the methylated aromatic hydrocarbons maybe freed from theexcess of the originally charged aromatic hydrocarbon and then beseparated into desired fractions or individual compounds by distillationat ordinary or reduced pressure or by other suitable means.

Methylation of aromatic hydrocarbons of the types hereinabove set forthare also carried out in the presence of hydrogen or of ahydrogencontaining gas. There is less formation of caricon and heavyhydrocarbonaceous material upon the catalyst when these conversionreactions are carried out under hydrogen pressure but carbon gen atomthan does benzene.

formation does occur to a substantial extent the absence of addedhydrogen.

The process of this invention may also be applied to the alkylation ofaromatic hydrocarbons with ethanol or with other primary alcohols whichordinarily are diflicult to react with aromatic hydrocarbons.

Methyl ether generally appears as a by-product of the methylation ofbenzene with methanol in CHQOH HOP(OH): -r CHaOP(H)2 H I; (2)Methylation: C6H6 cHiol wfln camera H0P'(0H)2 (3) Ether formation:

onion cmol wonn CHsOC-Hs no nomi Chemical decomposition of the methylester of phosphoric acid apparently occurs more readily by ithe reactionwith methanol than with benzene since the former has a more reactivehydro- Hence a higher temperature is required for methylation than forether formation,

The use of a solid phosphoric acid catalyst permits the process of thepresent invention to be carried out continuously with a fixed catalystbed and thus avoids mechanical problems and controls the time of contactof the reactants with the catalyst to form substantially the monomethylderivative of the aromatic hydrocarbon charged rather than more-highlymethylated compounds. For the present purpose solid phosphoric acidcatalyst has the advantage over composites of aluminum chloride andcarriers in that the solid phosphoric acid catalyst forms substantiallyno addition compounds or complexes with aromatic hydrocarbons ormethylated aromatic hydrocarbons.

The following examples are given to illustrate the character of resultsobtained by the use of the present process, although the data presentedare not introduced with the intention of unduly limiting the generallybroad scope of the invention.

Example I 80 parts by weight of benzene, 20 parts by The reacof toluene,xylenes, and higher methylated benzenes obtained were 16, 8. and 36% ofthe theoretical based upon the amount of methanol available.

Example If 5.5 parts by weight of toluene, 1.0 part by 4 weight ofxylenes, and 2.5 parts by weight of more-highly methylated benzenes wereobtained when 88 parts by weight of benzene, 23 parts by weight ofdi-methyl ether, and'10 parts by weight of 10-12 mesh solid phosphoricacid catalyst -were heated in the presence of hydrogen at 400 C. for 4hours under a maximum matic hydrocarbons which comprises subjecting anaromatic hydrocarbon to contact with a methylating agent at atemperature of from about 350 to about 500 C. in the presence of acatalyst comprising essentially a calcined com posite of an acid ofphosphorus and a generally siliceous adsorbent capableof undergoingcompound formation with said acid of phosphorus.

3. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbonto contact with amethylating agent at a temperature of from.

about 350 to about 500 C. in thepresence of a catalyst comprisingessentially a calcined composite of pyrophosphoric acid and diatomaceousearth.

4. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon to contact with amethylating agent at a temperature of from about 350 to about 500 C. inthe presence of a catalyst containing as its active ingredient anacid-acting salt of phosphorus 5. A process for producing methylatedaromatic hydrocarbons which comprises subjecting an aromatic hydrocarbonto contact witha methylating agent at a temperature of from about 350 toabout 500 C. under a pressure of from substantially atmospheric toapproximately 300 atmospheres in the presence of a catalyst containingas its active ingredient an acid-acting compound of phosphorus.

6. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon to contact with methanol ata temperature of from about 350 to about 500 C. under'a pressure of fromsubstantially atmospheric to approximately 300 atmospheres in thepresence of a catalyst containing as its active ingredient anacid-acting compound of phosphorus.

7. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon to contact with methylether at a temperature of from about 350 to about 500 C. under a.pressure of from sub- 350 to about 500 C. under a pressure of from'substantially atmospheric to approximately 300 atmospheres in thepresence of a catalyst containing as its active ingredient anacid-acting compound of phosphorus.

9. A process for producing methylated aroinatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon, hydrogen, and amethaylatin agent to contact at a temperature of from about 350 to about500 C. in the presence of a catalyst containing as its active ingredientan acid-acting compound of phosphorus.

10. A process for producing methylated aro-' matio hydrocarbons whichcomprises subjecting an aromatic hydrocarbon, hydrogen, and amethylating agent to contact at a temperature of from about 350 to about500 C. in the presence of a catalyst comprising essentially a calcinedcomposite of an acid of phosphorus and a generally siliceous adsorbentcapable of undergoing com- I acid-acting salt of phosphorus.

12. A process for producing a substantial yield of toluene from benzenewhich comprises sub-' Jecting said benzene, hydrogen, and a methylatlngagent to contact at a temperature of from about 350 to about 500' C. inthe presence of a catalyst containing as its active ingredient anacidacting compound of phosphorus.

13. A process for producing a substantial yield of toluene from benzenewhich comprises subjecting said benzene, hydrogen, and a methylatingagent to contact at a temperature of from about 350 to about 500 C.under a pressure of from substantially atmospheric to approximately 300.atmospheres in the presence of a catalyst containing as its activeingredient an acid-acting compound of phosphorus.

14. -A process for producing a substantial yield of toluene from benzenewhich comprises subjecting said benzene, hydrogen, and methanol tocontact at a temperature of from about 350 to about 500 C. under apressure of from substantially atmospheric to approximately 300atmospheres in the presence of a catalyst containing as its activeingredient an acid-actin compound of phosphorus.

15. A process for producing a substantial yield of toluene from benzenewhich comprises subjecting said benzene, hydrogen, and methyl ether tocontact at a temperature of from about 350- to about 500 C. under apressure of from substantially atmospheric to approximately 300atmospheres in the presence of a catalyst containing as its activeingredient an acid-acting compound of phosphorus.

16. A process for producing a substantial yield of toluene from benzenewhich comprises subjecting said benzene, hydrogen, and a methyl halideto contact at a temperature of from about 350 to about 500 C. underapressure of from substantially atmospheric to approximately 300atmospheres in the presence of a catalyst containing as its activeingredient an acid-acting compound of phosphorus.

1'7, A process for producing a substantial yield of toluene from benzenewhich comprises subjecting said benzene, hydrogen, and methanol tocontact at a temperature of from about 350 to about 500 C. under apressure of from substantially atmospheric to approximately 300atmospheres in the presence of a catalyst comprising essentially acalcined composite of an acid of phosphorus and a generally siliceousadsorbent. "18..A process for producing a substantial yield of toluenefrom benzene which comprises subjecting'said benzene, hydrogen, andmethanol to contact at a temperature of from about 350 to about 500 C.under a pressure of from substantially atmospheric to approximately 300atmospheres in the presence of a catalyst comprising essentially acalcined composite of pyrophosphoric acid and diatomaceous earth.

19. A process for producing a substantial yield of toluene from benzenewhich comprises subjecting said benzene, hydrogen, and methanol tocontact at a temperature of from about 350 to about 500 C. under apressure of from substantially atmospheric to approximately 300atmospheres in the presence of a catalyst containing as its activeingredient anacid-acting salt of phosphorus.

20. A continuous process for producing toluene from benzene whichcomprises subjecting from 1 to about 20 molecular proportions of saidbenzene and 1 molecular proportion of methanol to contact at atemperature from about 350 to about 500 C. under a pressure of fromsubstantially atmospheric to approximately 300 atmospheres in thepresence of hydrogen and of a catalyst containing as its activeingredient an acid-acting compound of phosphorus to form a. productcontaining a substantial proportion of toluene; separating said productinto unconverted benzene,

toluene, and poly-methylated benzenes; and recycling said unconvertedbenzene and polymethylated benzenes to commingle with the methanol andbenzene being charged to contact with the catalyst.

21. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon to contact with methanol ata temperature of from about 350 to about 500 C. in the presence of acatalyst comprising essentially a calcined composite of an oxy-acid ofphosphorus and a generally siliceous absorbent capable of undergoingcompound formation with said oxy-acid of phosphorus.

22. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon to contact with dimethylother at a temperature of from about 350 to about 500 C. in the presenceof a catalyst comprising essentially a calcined composite of an oxy-acidof phosphorus and a generally siliceous absorbent capable of undergoingcompound formation with said oxy-acid of phosphorus.

23. A process for producing methylated aromatic hydrocarbons whichcomprises subjecting an aromatic hydrocarbon to contact with amethylating agent at' a temperature of from about-350 to about 500 C. inthe presence of a catalyst comprising essentially a calcined compositeof pyrophosphoric acid and a generally siliceous adsorbent capable ofundergoing compound formation with said pyrophosphoric acid.

24. A process for producing methylated aro- TENT matic hydrocarbonswhich comprises subjecting STATES PA s an aromatic hydrocarbon tocontact with a Number Name 1 Date methylating agent at a temperature offrom .1 0 cb llkopf y 1 about 350 C. to about 500 C. in the presence of1.951.123 Barbier M r- 1 1 4 acaicined catalyst comprising essentiallyan oxy- .1 1 l t ADr- 1 acid of phosphorus and a generally silicious ab-34 1 randt me 1 sorbent capable of undergoing compound formation withsaid oxy-acid of phosphorus. FOREIGN PA 30 Number Country Date LOUIS scm464,752 Great Britain Apr. 19, 1937 478,424= Great Britain Jan. 14, 1938REFERENCES CITED o'rr-mn moms The following references are of record inthe Shen et ai., Jour. Inst. Pet. Tech., volume 26.

file of this patent: 4'zs-4ao (mo).

